The present invention relates to a non-volatile memory device and a method for manufacturing a non-volatile memory device and, more particularly, to a non-volatile memory semiconductor device having a nitride-oxide dielectric layer and a method for manufacturing a non-volatile memory device having a nitride top dielectric layer.
Non-volatile memory (“NVM”) is a semiconductor memory device that is capable of storing the programmed data or information even when electricity supplied to it is removed from a device containing the NVM memory. Examples of NVM include Mask Read-Only Memory (Mask ROM), Programmable Read-Only Memory (PROM), Erasable Programmable Read-Only Memory (EPROM), and Electrically Erasable Programmable Read-Only Memory (EEPROM). Typically, NVM can be programmed with data, read and/or erased, and the programmed data can be stored for an extended period of time before being erased, such as ten years.
An example of an NVM includes Nitride Read Only Memory, which is a type of EEPROM that uses a silicon nitride layer as a charge-trapping layer to store data. Other charge-trapping materials may be used for forming NVM devices. An example of Nitride Read Only Memory cell design includes a metal-oxide-silicon field effect transistor (MOSFET) having an ONO (oxide-nitride-oxide) layer disposed between the gate and the source/drain of the semiconductor material. The nitride layer in the ONO layer is able to “trap” charge (electrons) when the device is “programmed.” Charge localization is the ability of the nitride material to store the charge without significant lateral movement of the charge throughout the nitride layer. Nitride Read Only Memory utilizes a relatively thick tunnel oxide layer, which typically negatively impacts the time it takes to erase a memory cell. Nitride Read Only Memory can be contrasted with conventional “floating gate” memory cells wherein the floating gate is conductive and the charge is spread laterally throughout the entire floating gate and charge is transferred through a tunnel oxide layer. Also, Nitride Read Only Memory can be repeatedly programmed, read, erased and/or reprogrammed by known voltage application techniques.
To provide a non-volatile memory device, it is therefore desirable to provide a non-volatile memory semiconductor device that has good charge retention ability or reduced charge loss compared to some of the conventional NVM, such as certain Nitride Read Only Memory devices. It is also desirable to provide an NVM that can be operated with adequate speed, such as that needed when erasing old information or in programming new information.